1. Field of the Invention
The present invention relates to a method for forming a capacitor of a semiconductor device, and more particularly to a method for forming a capacitor of a semiconductor device, which can sufficiently secure necessary charging capacity and also improve current leakage prevention characteristics.
2. Description of the Prior Art
Recently, as the high integration of a memory product accelerates due to the development of the semiconductor process technology, the unit cell area decreases and the operation voltage lowers. However, in spite of the decrease of the cell area, there has been continuous demands for a memory device having a sufficiently high charging capacity of at least 25 fF per cell for the operation thereof, in order to prevent the generation of soft error and the reduction of refresh time.
Therefore, in case of a NO (Nitride Oxide) capacitor for DRAM which employs a dielectric body formed of an Si3N4 dielectric layer deposited by using DCS (Di-Chloro-Silane) gas, a charge storage electrode of three dimensional shape which has an electrode surface of semi-spherical shape having a wide surface area is used, and the height thereof continuously increases in order to secure a sufficient capacity.
On the other hand, the NO capacitor shows a limit in securing a charging capacitance of over 256 M needed for a next-generation DRAM product. Therefore, as shown in FIG. 1, capacitors employing a single dielectric layer 5 made from a high dielectric material such as Ta2O5 (∈=25), Al2O3 (∈=9), and HfO2 (∈=20) have been actively developed in order to secure a sufficient capacity. Recently, capacitors using an La2O3 (∈=27) dielectric layer are also being developed.
In FIG. 1, the reference numeral 1 represents a semiconductor substrate, 2, an isolation interlayer, 3, a storage node contact, 4, a storage electrode, and 5, a plate node.
However, since the dielectric constant of an Al2O3 dielectric layer is not very large, there is a limit in securing the charge capacitance by the Al2O3 dielectric layer. In HfO2 and La2O3 dielectric layers whose dielectric constant are larger than that of the Al2O3 dielectric layer, if the equivalent SiO2 thickness of the capacitor is lowered to about 15 Å, the leakage current rapidly increases and the yield electric field strength dramatically lowers. As a result, the layers are vulnerable to repetitive electric impacts and the endurance of the capacitor deteriorates.